Synoptic monitoring of vegetation dynamics relies on satellite observations of the distinctive spectral contrast between red and near infrared reflectance that photosynthetically active green vegetation exhibits. It has long been recognized that the Normalized Difference Vegetation Index (NDVI) suffers a rapid decrease of sensitivity at moderate-to-high densities of photosynthetic green biomass. This decrease can conceal detection of vegetation change in croplands, woodlands, and productive grasslands. We applied a recent, straightforward modification of the NDVI, the Wide Dynamic Range Vegetation Index (WDRVI), to a standard AVHRR dataset to assess its sensitivity to variability within ecoregions and across years, relative to NDVI. In productive ecoregions, the sensitivity increased within a single year by up to 47% and the sensitivity to interannual variability increased by up to 100%. The WDRVI exhibited no increase in sensitivity in ecoregions with sparse vegetation. These findings have significant implications for diverse applications of vegetation monitoring products.
